Well, Hebrew doesn't write vowels most of the time, they're implied. Alef (א) is actually the sound of silence, followed by a vowel. For right now, you can just guess A and be right a lot of the time, but you'll get used to reading after a while. If it comes before a waw (vav, ו) it's O or U, like in או.
I was struggling to understand why "או" is pronounced "o". It says in the tips and notes that "א - Aleph" is silent and that "ו - Vav" is pronounced "v". However, I found this useful video which that "ו" can be pronounced "v", "o", and "u", which helps explain why it's pronounced "o".
https://www.youtube.com/watch?v=kJUMyHR0zN4 I hope that helps and recommend giving some of the videos a watch.
I'm under the impression that all courses on a particular app. use the heart system. If you use your computer, or the computer function of your cell phone, you won't have to deal with the heart system. If you go into the "Tips" section, which one of the apps does not have, you will see charts explaining the pronunciation of the letters.
The natural way to spell "o" as a word is "או", so I'm not sure what you find strange here.
Having said that, in Arabic this word is pronounced with the diphthong a-u (as in English "how"). To take a wild guess (I'm not a linguist), in very ancient Hebrew or proto-semitic it was this diphthong, and then Hebrew (or some ancestor of it) contracted it to sound "o" as happens often in many languages (most "au"s in English, for example). That must have happened before the nikkud was invented in the 11th century.
That is a weird question to ask, my friend. The safest and least speculative answer is … because, that is just the way Hebrew is. And most people I know, definitely most people here on Duolingo, as I have already had the chance to find out, would just be happy with that. …not me, though, but to be perfectly honest, the following 3 analyses I came up with are just pure speculation. Anyway, I got so intrigued by that question that I could not help but share these speculations with you.
1) sound symbolism: [ee] is a higher pitched sound, or perceptually “thinner”, as it were, representing the female principle; [ah] is a deeper, “thicker”, lower-pitched sound representing the male principle (this is a physiological metaphor, or some such, fill in the blanks as to why for yourself).
2) phonetic perception (a kind of follow up on the first hypothesis): as [m] (nasal bilabial stop, voiced) and [b] (oral bilabial stop, voiced) have the same place of articulation and only differ in the fact that [m] is nasal and [b] is oral, if we assumed that the starting point was something like [ʔm-] vs [ʔb-], in order to supplant the vowel between the two consonants (for ease of articulation or some such), that is [ʔVm-] and [ʔVb-], [ma] naturally creates a higher pitch sound than [ba] such that the high(est) vowel [i] matches the former and the low(est) vowel [a] the latter (a sort of a pitch harmony = I made that up) resulting in [ʔim-] vs [ʔab-]. Actually, in Arabic the vowel for mother is [u], i.e. [ʔumm(un)], which is also a high vowel (the third in the triangle /a, i, u/, so the theory works for the Arabic word, as well. In fact, it is not clear which vowel to reconstruct for Proto-Semitic here, since some Semitic languages have /i/ (or its continuation), and some have /u/ (or its continuation) – see further below for more.
3) historical development (I believe the most likely one of these speculations). These two words actually started quite differently: “mother” is to be reconstructed as (either) [ʔimm-] (or [ʔumm-], as already alluded to) but “father” as [ʔab-]. Therefore it is likely that /i/ (or /u/) in the word for “mother” is a helping vowel, to break the consonantal cluster (hence the variation within Semitic), i.e., [ʔmmV-] which was at some point a perfectly normal word (cf. Berber languages with all the consonant clusters, some words can be just consonants), but at some point, “mother” acquired a helping vowel (ie. [ʔimm-] in Aramaic and Hebrew and [ʔummu-] in Ugaritic, Akkadian and Arabic. Now, for “father”, there are actually 5 forms of this root altogether, enlarged by other consonants: [ʔbw-], [ʔby-], [ʔbh-], [ʔbt] (yes, I know, weird, vocative in Quran is [ʔabata] ‘father!’) but also just a basic [ʔab-] (Biblical Hebrew [ʔav]). So it seems that the most primitive (internal) reconstruction for “mother” and “father” is [ʔmm-] vs. [ʔab-], in which [a] is actually a full vowel. In other words, [a] was in the word for “father” before there was [i] (or [u]) in the word for “mother”. So we are pretty much where we started, because now we could also just ask WHY? … hm … :)
Fun fact: actually Modern Hebrew [aba], and also [eema] here, are loans from Aramaic, or Jewish Aramaic to be precise, [ʔabbaʔ] is etymologically either from [ʔabhaʔ] or [ʔabwaʔ]. The Biblical Hebrew word for father is [ʔav] (plural [ʔav-oθ]) and mother is [ʔemm], with closed [e] from earlier [i], which was preserved in Aramaic as such, obviously, and in the Biblical Hebrew plural [ʔimmahoθ] (θ as the first sound of 'think').